1. Field of the Invention
The present invention relates to a light emitting device usable for a lighting device such as an LED bulb, a display unit, a display, the back light source of a liquid crystal display, and the like.
2. Description of the Related Art
In recent years, various kinds of light emitting devices using LEDs (light emitting diodes) as light emitting elements have been developed, because the amount of heat generation and the power consumption by LEDs are smaller than those of light sources by a filament bulb or the like, and LEDs have a longer life.
For example, Unexamined Japanese Patent Application Publication No. 2006-295085 presents a light source unit, with light emitting diodes, that is provided with a base plate on which a plurality of light emitting diode elements are mounted, a printed board arranged on the top surface of the base plate, and cathode/anode terminal electrodes formed on the printed board such as to sandwich the area where the plurality of light emitting diode elements are mounted.
Further, Unexamined Japanese Patent Application Publication No. 2010-034487 presents a light emitting device provided with a substrate on which a glass layer is formed, a plurality of LED chips arranged on the glass layer, and the external connection terminal of a positive electrode and the external connection terminal of a negative electrode formed on the glass layer such as to sandwich the plurality of LED chips.
Still further, to prevent an LED chip from being damaged by high-voltage static electricity, Unexamined Japanese Patent Application Publication No. 2007-227882 presents an LED package provided with an ESD protecting section, with a zener diode or the like, that is arranged in an area where the lead frame on the anode side and the lead frame on the cathode side are adjacent to each other.
Light emitting devices with arrangement of several tens of light emitting elements on a substrate have been widely developed to improve the brightness of a light emitting device. For such a light emitting device having a plurality of light emitting elements mounted thereon, it is recommended to arrange a protection element, such as the above-described zener diode, on the substrate so as to prevent element destruction and deterioration of performance which could occur when an over voltage is applied to the light emitting elements on the substrate.
However, in a conventional technology, the position of arranging a protection element has not been sufficiently considered in a case of arranging a plurality of elements on a substrate. For example, in the Unexamined Japanese Patent Application Publication No. 2006-295085 and the Unexamined Japanese Patent Application Publication No. 2010-034487, using a protection element is not considered at all, and no means have been presented for preventing element destruction and the deterioration of performance which can occur when an over voltage is applied to a plurality of light emitting elements. Further, in Unexamined Japanese Patent Application Publication No. 2007-227882, only the position of arranging a protection element in a case of mounting a single light emitting element is considered, and no consideration is made regarding a case of arranging a plurality of light emitting elements on a substrate.
The present invention has been developed, addressing the above-described problems, and an object of the invention is to provide a light emitting device with a plurality of light emitting elements arranged on a substrate, wherein a protection element with a zener diode or the like can be arranged at an appropriate position.